Our website is intended for adults only (18+)

By using this website, you confirm that you are 18 years or older and agree with our Privacy and Cookie Policy

EUR English

Fact or Fiction: How to Reach a Gram Per Watt

Last updated: 26 September 2023

How to Reach a Gram Per Watt

“A gram per watt” – you may have heard this phrase mentioned in hushed whispers at your local hydroponic store. But what does it really mean, and is it even possible to achieve?

Gram Per Watt: Myth or Reality?

The infamous “gram per watt” metric has been around for almost as long as cannabis itself. The adage states that, when everything goes according to plan, a grower can harvest at least one gram of marijuana per watt of light they use in their garden. At this rate, the yield per plant for a 600w garden would reach 600 grams.

Gram Per Watt: Myth or Reality?

This is a nice goal to strive for, but it’s not easy. Many newbie growers hear about the gram per watt of light metric and hold themselves to that standard right away. Don’t do this! It’s far more likely that your garden will yield 0.5 – 0.75 per watt.

Still, don’t give up just yet. If you work diligently, you too can reach the legendary 1 gram per watt milestone.

What Stands Between You and a Gram Per Watt

To reach yields of this size, you’ll need to focus on four things. First, develop your skills and experience. Second, pick the right strains for the job. Third, don’t waste your time with weak genetics – you need the best. Finally, you need to fine-tune your growing setup. If you can do all that, you’ll be well on your way to harvesting a gram per watt.

Skills and Experience

You may think you’ve read every book on cannabis. You’ve spent countless hours watching videos online. What’s more, you’re even reading this article!

It doesn’t matter how much research you put into growing before you start – you’re going to make a few mistakes on your way to 1 gram per watt. Working in a cannabis garden is like working in a commercial kitchen; in both settings, you need to be able to identify problems quickly and act on reflex. This is a process you can only learn through repetition and practice.

Even experienced growers can fall into this trap, particularly when they’re working in new environments. You could be a 20-year growing veteran and still need to put a few harvests under your belt before getting used to a new garden.

how many plants should per square meterREAD NOW

Wrong Strains

This is a common error that growers new and old make while striving for a gram per watt. Certain strains will never provide the yields you’re looking for.

Gramm Per Watt Sativa

Gramm Per Watt Indica

For example, many sativa strains grow long, thin, and lanky, with small, dense buds spread apart on the stem. Although these strains can provide top-tier quality, they just can’t hit the weight you’re looking for. In contrast, indica strains (or hybrids with indica genetics) grow low, bushy, and fat. That makes them much better suited for 1 gram per watt yields.

Poor Genetics

Choosing the right plants can go deeper than choosing the right strains. Sometimes, two different phenotypes will exhibit different physical traits – even though they’re technically the same strain! One of those varying traits can be yield, which is critical when it comes to hitting a gram per watt.

As a result, you’ll need to be extremely strict when choosing plants for a gram-a-watt garden. For example, photoperiod genetics have a slight advantage over autoflowering strains. You can veg photoperiodic strains for more time, meaning the plants themselves will be bigger in the flower phase. This sets them up to throw down serious weight on harvest day.

Growing Setup

Reaching a gram per watt isn’t just about selecting the best strains and phenotypes for the job – you’ll also need the right gear for your garden. It’s an unfortunate fact of life that money can make things easier, and that’s especially true with a cannabis garden.

Weed Growing Setup

You’ll need everything dialed in perfectly to pull it off. That includes using the best lights, buying high-end climate control gear, and even using CO2 to maximize your yields. Additionally, using premium nutrients will go a long way towards achieving a gram-per-watt garden.

Tips for Achieving 1 Gram Per Watt (And More)

In this section, we’ll cover some helpful tricks that can help you achieve a gram per watt. If you’re lucky, you might even be able to get higher yields – perhaps even up to 2 grams per watt!

Dial in All Environmental Variables

We cannot stress this enough: if you want to increase yields, you’ll need to control your growing environment. Here are a few tips to keep in mind while you’re setting up your garden:

  • Humidity – when they’re young, plants like wet environments. But as they age, they come to prefer a drier climate. For seedlings and plants in the veg stage, start with 80 percent humidity and taper off to 60 percent by the end of veg. Then, maintain an RH of 40-50 percent throughout the flower cycle.
  • Temperature – like humidity, temperatures should be tapered. Start with 85°F (30°C) in the early veg phase, and lower that to 80°F (26.6°C) by the end of veg. Stay around 75-78°F (25-26°C) until late flower, when you can taper down to 68-70°F (20-21°C) to increase yields.
  • Airflow – in the outside world, your plants would experience wind and weather. Of course, that won’t happen naturally in your garden. Fortunately, wind is easy to simulate – you’ll just need to set up some rotating fans!

Get the Best Growing Light You Can Afford

Pop quiz: what’s the single most important factor when it comes to hitting a gram per watt? If you guessed light, you’re correct! Choosing the right grow lamp is a critical part of achieving this lofty goal.

LED Growing Light

HSP Growing Light

Some people believe it’s impossible for growers to reach a gram per watt if they’re using an LED light. That’s not exactly true, but it will make your task significantly more difficult. Instead, choose HPS (high-pressure sodium) grow lamps. These lights are less efficient (and more expensive), but they can super-charge cannabis plants with the power they need to increase their yield.

grow lightsREAD NOW

Use All of Your Growing Space

When you’re growing indoors, every inch counts. That’s particularly true when you’re trying to maximize your garden’s yield. Train your plants to grow outward, not upwards. We’ll cover some specific plant training techniques later in this guide.

Weed Growing Space

Pick a High-Yielding Strain

Remember how we mentioned that choosing plants with the right genetics was critical to achieving a gram per watt? You didn’t think we’d leave you hanging, did you? Here are a few strains that we believe can hit that milestone.

You may notice that most of these strains are hybrids. There’s a reason for that – since you’re growing indoors, indicas can help you make the most of your vertical space. But we didn’t want to only include pure indicas, either; after all, there’s more to being high than couch lock and the munchies.

Glookies (Barney's Farm) Glookies (Barney's Farm)
  • Photoperiod
  • Begin your own mind trip
  • 700 - 800 g/m² indoors
    2000 - 3000 g/plant outdoors
  • 25 %
View strain


Here’s a strain that combines peerless quality with a possible gram per watt yield. This Gorilla Glue x Thin Mint GSC cross can yield between 700 and 800 grams per square meter indoors, making it perfectly capable of hitting that milestone under the right conditions. What’s more, Glookies’ 25 percent THC level bestows it with a pleasant high, making it highly rewarding to grow.

Pure Kush (GHS) Pure Kush (GHS)
  • Photoperiod
  • When you need a vacation
  • 19.35 %
  • 900 g/m² indoors
    900 g/plant outdoors
Out of stock
View strain

Pure Kush

Though its name might imply otherwise, Pure Kush isn’t “pure.” Instead, its genetics are only 70 percent indica-dominant. Fortunately, that’s still enough to yield 1 gram per watt. Meanwhile, this strain’s 30 sativa lineage may not sound like much, but it helps round out this hybrid’s effects with an invigorating and creative burst.

Monster Profit (Heavyweight Seeds) Monster Profit (Heavyweight Seeds)
  • Photoperiod
  • 22 %
  • Mind clarification
  • 800 g/m² indoors
    1000 g/plant outdoors
View strain

Monster Profit

If you’re looking for a sativa-dominant strain capable of yielding a gram per watt, Monster Profit is your girl. This photoperiodic strain is equally at home indoors and outside. You wouldn’t normally be able to get yields this impressive from an Amnesia Haze descendant, but Monster Profit benefits from the indica-heavy genes of its other parent, Dream Machine.

Super Critical Bud CBD (Garden of Green) Super Critical Bud CBD (Garden of Green)
  • Photoperiod
  • 25 %
  • Heals body and mind
  • 750 g/m² indoors
Out of stock
View strain

Super Critical Bud CBD

Not many CBD-heavy strains are capable of throwing down 1 gram per watt on harvest day – but that’s exactly what you could get with Super Critical Bud CBD. This marijuana mutt combines Afghan Skunk #1, Mexico, Columbia, Durban, and Kush genetics. Somehow, all those genes manage to coalesce into a huge yielder, containing a CBD level of up to 23 percent and a 25 percent THC level.

Bruce Banner #3 (Original Sensible Seeds) Bruce Banner #3 (Original Sensible Seeds)
  • Photoperiod
  • 800 g/m² indoors
    1000 g/plant outdoors
  • 28 %
  • A good balance between high and stone
View strain

Bruce Banner #3

No list of gram per watt strains would be complete without Bruce Banner #3. This strain’s name is literally inspired by how big and green it gets, boasting yields reaching 800 grams per square meter. What’s more, Bruce Banner #3’s 28 percent THC level makes it the most potent high-yielding strain on this list.

high yield strainsREAD NOW

Dial in Your Nutrient Regimen

A plant can only get as big as you let it! Dialing in your nutrient balance is critical to achieving a gram per watt. Since you’re aiming for big flowers, you’re going to want to boost nutrients like phosphorus and potassium. Many nutrient lines offer a “PK Booster” for use in the mid to late flower phase (P is Phosphorus, K is Potassium).

On the other hand, don’t overdo it with PK Boosters. Forcing too much potassium or phosphorus into your plants will trigger nutrient lockout, which is essentially a nutrient overdose. This is important to avoid since plants won’t be able to uptake new nutrients if they’re locked out. The manufacturer will give you dosing instructions on the bottle – use these as a guide.

Take Care of Your Plants DAILY

Any grower aiming for 1 gram per watt needs to keep a watchful eye on their plants. That’s because it doesn’t take long for problems in a garden to spiral out of control. Because you’re reaching for such a lofty goal, any issue – no matter how insignificant – can throw a monkey wrench into your plans. That’s why it’s so important to nip problems in the metaphorical bud well before they can affect your yields.

Train Your Plants

Earlier in this article, we told you that using every inch of your garden is an important trick to keep in mind while working to increase yield. Here, we’re going to give you some ideas on how to do just that!

Growing weed without training

Train Your Plants

  • LST/HST – these training methods both involve spreading a plant’s branches out when it’s younger. However, the techniques involved in these methods differ. To learn more, check out our complete guide to HST/LST.
  • Topping – a technique where the grower prunes the top of branches during the veg cycle to create two larger branches. We explain it in-depth here.
  • ScrOGging – a somewhat advanced technique that involves spreading plants out using a grid of trellis wire to increase yield. Learn more with our breakdown.

Properly Prepare the Plant for the Flower Phase

If you’re striving for a high-yielding garden, you need to give your plants all the help they can get. As part of this, be sure to prune away lower branches before plants reach the flower phase. By eliminating lower branches before flowering, you’ll encourage your plants to focus all their nutrients and energy on their upper canopy – the part that’s closest to your light source.

Don’t Switch to 12/12 Too Early

We already mentioned that you should choose photoperiodic strains to increase cannabis yields, and this is why. By letting your plants veg out for longer, you’ll allow them to develop longer branches with more bud sites. That sets them up nicely to throw down some serious weight on harvest day. (If you must use an LED lamp, this is a good way to boost your LED yield per watt.)

Boost the Yield During Flowering

One last tip for boosting your yield in the flower phase is to defoliate your plants. Do this whenever you notice light failing to penetrate through your canopy. Bud sites beneath a plant’s canopy need all the light they can get – otherwise, they’ll just grow larf.

Don’t overdo it with defoliation, though. Remember: your plants’ leaves help them harness the power of your lights. That’s the most important ingredient when you’re trying to boost yields!

Fight For Your Right to A Gram Per Watt of Light

It may be a difficult feat, but you really can achieve a gram per light – possibly, even 2 grams per light! Just keep in mind everything we mentioned in this article. You definitely have your work cut out for you, but if you stick with it, your yields will thank you. Good luck!

Herbies Head Shop expressly refuses to support the use, production, or supply of illegal substances. For more details read our Legal Disclaimer

If its a cheap chinese brand that says 300 watts, it more then likely pulls anywhere from 60-150 watts from the wall and personally thats where i would begin to calculate is the actual power draw. ive never fully achived 1 gram per watt but im working on it.
Joshua Arreguin
Without a wattage meter, to know how much watts you were using you can't make a meaningful calculation. Step 1, get a wattage meter.
Jay Jay
Thanks to you, I feel more confident when it comes to doing another grow. My first grow was a bit shabby. So, I started doin more research, and I feel like I know a lot more now. Thanks!!!
Add a comment

How to post a comment

Thank you for leaving a comment for us!

Your feedback will be posted shortly after our moderator checks it.

Please note that we don’t publish reviews that:

  • Are written in ALL CAPS
  • Use aggressive or offensive language
  • Promote other websites (include contact details or links)